Proof: integration from 0 to pi/2 of sin^2n xdx = (1.3.5.7...(2n-1))/(2.4.6.8...... x n/2?

I need it to be done only using integration by parts and substitution thou. I know how to do it with the formula. But I got confused when I have to use only integration by parts and substitution.
Update: The x after = sign is meant to be * (times sign)
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