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6th Year HL · Mathematics
Integrals · Antiderivatives

Integration of trigonometric functions

$\sin^2 x$, $\tan^3 x\cdot\sec^2 x$ or $\cos(4x-1)$ are not in the table of standard integrals as they stand. But with a trigonometric identity, or by spotting the hidden chain, they turn into something that is. There is no new technique here: it is just the table of standard integrals in the Formulae and Tables booklet plus trigonometric identities from 5th Year. Think of a ramp in a skatepark in Cork whose slope is given by $\sin^2 x$: how would you find its height? We come back to it below.

First check whether it is the chain in disguise

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Find the indefinite integral of the following function, noting that it is a composite function containing the derivative of the argument:…

Find the indefinite integral of the following function, noting that it is a composite function containing the derivative of the argument:

$\int x \times \sin(x^2 + 3) \, dx$

Solve

Disguised power: $\sin^n x\cdot\cos x$ and similar

Flow diagram showing the integration of tangent cubed times secant squared, identifying u as tangent and applying the composite power rule. tan³x · sec²x u=tan x, u'=sec²x tan⁴x / 4 + C rule uⁿ·u'
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Find the indefinite integral of the function $f(x) = \tan^3(x) \times \sec^2(x)$. Remember to check whether the expression fits a power-type integral where a function is…

Find the indefinite integral of the function $f(x) = \tan^3(x) \times \sec^2(x)$. Remember to check whether the expression fits a power-type integral where a function is raised to an exponent and multiplied by its derivative.

Solve

Identities to remove even powers: $\sin^2$, $\cos^2$, $\tan^2$

Odd powers of sine or cosine

For an odd power of cosine, do the same with $\cos^2 x = 1-\sin^2 x$ and $u=\sin x$. The same trick works with negative or fractional powers, e.g. $\dfrac{\sin^3 x}{\sqrt{\cos x}}$ uses $u=\cos x$.

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On many occasions, trigonometric identities allow us to transform a difficult expression into an immediate one. Use the relation $\tan^2(x) + 1 = \sec^2(x)$ to calculate…

On many occasions, trigonometric identities allow us to transform a difficult expression into an immediate one. Use the relation $\tan^2(x) + 1 = \sec^2(x)$ to calculate the following antiderivative:

$\int \tan^2(x) \, dx$

tan²(x) + 1 = sec²(x) tan²(x) = sec²(x) - 1 ∫ tan²(x) dx = ∫ ( sec²(x) - 1) dx
Solve
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An architecture firm is designing the profile of a ramp for an extreme sports park. The gradient of the ramp at each point $x$ is given by the function…

An architecture firm is designing the profile of a ramp for an extreme sports park. The gradient of the ramp at each point $x$ is given by the function $g(x) = \sin^2(x)$. If the ramp starts at the point $(0, 0)$, determine the function $G(x)$ that describes the height of the ramp at any point.

x y G(x) Height x Gradient g(x) = sin²(x) (0,0)
Solve
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Find the antiderivative of the function $f(x) = \frac{\sin^3(x)}{\cos^2(x)}$. Hint: As this is an odd function in $\sin(x)$, use the substitution $t = \cos(x)$.

Find the antiderivative of the function $f(x) = \frac{\sin^3(x)}{\cos^2(x)}$.

Hint: As this is an odd function in $\sin(x)$, use the substitution $t = \cos(x)$.

Solve
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Calculate the indefinite integral of the following trigonometric rational function. This type of integral frequently appears in the calculation of gravitational fields…

Calculate the indefinite integral of the following trigonometric rational function. This type of integral frequently appears in the calculation of gravitational fields in astrophysics:

$$I = \int \frac{\sin^3(x)}{\sqrt{\cos(x)}} \, dx$$

Note: Consider a substitution relating the trigonometric functions present and remember the fundamental trigonometric identity.

Solve

Combining identity and chain in a single integral

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To start practising finding antiderivatives, find the general antiderivative of the following function, which includes a linear adjustment in the argument of the cosine:…

To start practising finding antiderivatives, find the general antiderivative of the following function, which includes a linear adjustment in the argument of the cosine:

$f(x) = \cos(4x - 1)$

X Y 1 −1 1 −1 f(x) = cos(4x - 1) Δx=1/4 1/4 T = π/2 ∫
Solve
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Calculate the antiderivative of the following trigonometric function using fundamental identities to simplify the expression before integrating: $$f(x) =…

Calculate the antiderivative of the following trigonometric function using fundamental identities to simplify the expression before integrating:

$$f(x) = \frac{\cos^3(x)}{1 - \sin(x)}$$ x y π/2 π -π/2 -π 1 −1 f(x) = cos³(x) 1 - sin(x) Trigonometric identity: cos²(x) + sin²(x) = 1 Antiderivative ∫ f(x) dx = ?
Solve

Other methods: parts, product-to-sum and the $t$-substitution

Three more standard forms

The last idea also handles $\dfrac{\sin^{-1}x}{\sqrt{1-x^2}}$: let $u=\sin^{-1}x$, so $du=\dfrac{dx}{\sqrt{1-x^2}}$.

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Find the following indefinite integral using the natural logarithm in the result, recognising that the numerator is (almost) the derivative of the denominator:…

Find the following indefinite integral using the natural logarithm in the result, recognising that the numerator is (almost) the derivative of the denominator:

$\int \frac{\sin(x)}{5 + \cos(x)} \, dx$

Solve
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Find the family of antiderivatives of the following function using an appropriate substitution for even trigonometric functions in sine and cosine: $$f(x) =…

Find the family of antiderivatives of the following function using an appropriate substitution for even trigonometric functions in sine and cosine:

$$f(x) = \frac{1}{3\sin^2(x) + \cos^2(x)}$$

Suggestion: Divide the numerator and denominator by $\cos^2(x)$ to express the function in terms of $\tan(x)$ and its derivative $\sec^2(x)$.

Solve
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In the study of the oscillations of a suspension bridge, the acceleration of a point on the structure is given by the function $a(t)$. Find the velocity function $v(t)$…

In the study of the oscillations of a suspension bridge, the acceleration of a point on the structure is given by the function $a(t)$. Find the velocity function $v(t)$ knowing that the initial velocity is $v(0) = 0$ and the acceleration is:

$a(t) = \frac{\sec^2(t)}{\sqrt{4 - \tan^2(t)}}$

Hint: Be careful with the domains of the resulting functions.

Solve
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Calculate the indefinite integral of the function $f(x)$, which combines powers of inverse trigonometric functions and direct functions: $$I = \int \frac{\arcsen(x) +…

Calculate the indefinite integral of the function $f(x)$, which combines powers of inverse trigonometric functions and direct functions:

$$I = \int \frac{\arcsen(x) + x}{\sqrt{1 - x^2}} \, dx$$ x = −1 x = 1 x y 0 x ? y = f(x) I = ∫ f(x) dx = ? I = ∫ f₁(x) dx + ∫ f₂(x) dx
Solve
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Find the antiderivative of the function $h(x) = x^2 \times \cos(x)$ using the method of integration by parts. You will need to apply the method twice to reduce the…

Find the antiderivative of the function $h(x) = x^2 \times \cos(x)$ using the method of integration by parts. You will need to apply the method twice to reduce the degree of the polynomial until an immediate integral is obtained.

Solve
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In a physics experiment, the damped oscillation of a spring is analysed, where its vibration velocity as a function of time $t$ follows the function…

In a physics experiment, the damped oscillation of a spring is analysed, where its vibration velocity as a function of time $t$ follows the function $v(t) = e^{-t} \times \sin(2t)$. Determine the position function $s(t)$, knowing that this is a cyclic integral.

t v(t) ±e⁻ᵗ Equilibrium m v(t) s(t)=? v(t) = e⁻ᵗ · sin(2t) s(t) = ∫ v(t) dt = ? Note: Cyclic integral
Solve
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Find the antiderivative of the function $f(x)$ described below, using product-to-sum transformations: $$f(x) = \cos(5x) \times \cos(3x)$$ Once the family of…

Find the antiderivative of the function $f(x)$ described below, using product-to-sum transformations:

$$f(x) = \cos(5x) \times \cos(3x)$$

Once the family of antiderivatives is obtained, determine the one whose graph has an inflection point with a horizontal tangent at the point with abscissa $x = \frac{\pi}{2}$ and ordinate value $y = 2$.

Solve
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The "universal substitution" is a powerful tool for solving integrals of rational functions of sine and cosine. Use the substitution $t = \tan\left(\frac{x}{2}\right)$…

The "universal substitution" is a powerful tool for solving integrals of rational functions of sine and cosine. Use the substitution $t = \tan\left(\frac{x}{2}\right)$ to find the following antiderivative:

$$I = \int \frac{1}{1 + \sin(x) + \cos(x)} \, dx$$ x/2 1 t √(1 + t²) t = tan(x/2) sin(x) = 2t/(1+t²) cos(x) = (1-t²)/(1+t²) dx = 2dt/(1+t²)
Solve

Summary

See all the exercises in this section