Calculus
posted by Andre .
Use the integral identity:
∫(a1) (1/(1+x^2))dx=∫(11/a) (1/(1+u^2))du
for a>1 to show that:
arctan(a)+arctan(1/a)=π/2

after the integration, you have
arctan(1)  arctan(a) = arctan(1/a)  arctan(1)
π/4  arctan(a) = arctan(1/a)  π/4
rearrange the terms and you're done.
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