Indefinite Integration 1 Question 3

4. The value of 0[sin2x(1+cos3x)]dx, where [t] denotes the greatest integer function, is

(2019 Main, 10 April I)

(a) π

(b) 2π

(c) 2π

(d) π

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Solution:

  1. Given integral

I=02π[sin2x(1+cos3x)]dx=0π[sin2x(1+cos3x)]dx+π2π[sin2x(1+cos3x)]dx=I1+I2 (let) 

Now, I2=π2π[sin2x(1+cos3x)]dx

let 2πx=t, upper limit t=0 and lower limit t=π

and dx=dt

So, I2=π0[sin2x(1+cos3x)]dx

=0π[sin2x(1+cos3x)]dx

I=0π[sin2x(1+cos3x)]dx +0π[sin2x(1+cos3x)]dx

[from Eqs. (i) and (ii)]

=0π(1)dx][[x]+[x]=1,x Integer ]

=π



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