Olkoon x=(1-t^2)/(1+t^2) ja y=2*t/(1+t^2), missä t on reaaliluku. Sievennä lauseke x^2+y^2

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x^2=(1-t^2)^2/(t^2+1)^2

y^2=(4*t^2)/(t^2+1)^2

(1-t^2)^2+(4*t^2)=t^4+2*t^2+1=(t^2+1)^2

(t^2+1)^2/(t^2+1)^2=1