Question:

Find ∫(cos√x) dx=?

Updated On: Mar 3, 2024
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Solution and Explanation

\(I=\int cos\,x\,dx\)
Put 
\(\sqrt{x}=t\) so that 
\(\frac{1}{2\sqrt{x}}dx=dt\)
\(I=f(cos\,t)2tdt = 2\int tcos\,t\,dt\)
Integrating by parts, we get
\(I=2[tsin\,t-\int 1.sint\,dt]\)
=\(2[tsint+cost]\)
=\(2[x\,sin\,x+cos\,x]\).
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Concepts Used:

Trigonometric Equations

Trigonometric equation is an equation involving one or more trigonometric ratios of unknown angles. It is expressed as ratios of sine(sin), cosine(cos), tangent(tan), cotangent(cot), secant(sec), cosecant(cosec) angles. For example, cos2 x + 5 sin x = 0 is a trigonometric equation. All possible values which satisfy the given trigonometric equation are called solutions of the given trigonometric equation.

A list of trigonometric equations and their solutions are given below: 

Trigonometrical equationsGeneral Solutions
sin θ = 0θ = nπ
cos θ = 0θ = (nπ + π/2)
cos θ = 0θ = nπ
sin θ = 1θ = (2nπ + π/2) = (4n+1) π/2
cos θ = 1θ = 2nπ
sin θ = sin αθ = nπ + (-1)n α, where α ∈ [-π/2, π/2]
cos θ = cos αθ = 2nπ ± α, where α ∈ (0, π]
tan θ = tan αθ = nπ + α, where α ∈ (-π/2, π/2]
sin 2θ = sin 2αθ = nπ ± α
cos 2θ = cos 2αθ = nπ ± α
tan 2θ = tan 2αθ = nπ ± α