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Definite Integration question

2021 · 26 Feb · Shift 1 · Q37
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Definite Integration question

2021 · 26 Feb · Shift 1 · Q37

JEE MainMathematicsDefinite IntegrationNumerical+4 / −1
The value of the integral ∫0π∣sin⁡ 2x∣dx\int\limits_0^\pi {|{{\sin }\,}2x|dx}0∫π​∣sin2x∣dx is ‾\underline{\hspace{2cm}}​.
Numerical answer
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Correct answer: 2

  1. We need to evaluate I=∫0π∣sin⁡2x∣ dx.I=\int_0^\pi |\sin 2x|\,dx.I=∫0π​∣sin2x∣dx.

  2. Let u=2x  ⟹  du=2dx  ⟹  dx=du2.u=2x \implies du=2dx \implies dx=\frac{du}{2}.u=2x⟹du=2dx⟹dx=2du​. When x=0x=0x=0, u=0u=0u=0; when x=πx=\pix=π, u=2πu=2\piu=2π.

So, I=∫0π∣sin⁡2x∣ dx=12∫02π∣sin⁡u∣ du.I=\int_0^\pi |\sin 2x|\,dx=\frac12\int_0^{2\pi}|\sin u|\,du.I=∫0π​∣sin2x∣dx=21​∫02π​∣sinu∣du.

  1. Now use the standard result: ∫02π∣sin⁡u∣ du=4,\int_0^{2\pi} |\sin u|\,du=4,∫02π​∣sinu∣du=4, because over one full period, the area under ∣sin⁡u∣|\sin u|∣sinu∣ is 444.

Therefore, I=12⋅4=2.I=\frac12\cdot 4=2.I=21​⋅4=2.

  1. Hence the required integer value is 2.\boxed{2}.2​.
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