目測不好做,好像做起來有點(diǎn)不值當(dāng).做了就有上限250大神，題目不對(duì)，應(yīng)該是求a+b的值，肯定是90°(sina)^4/cos²b+(cosa)^4/sin²b=1為了方便，換元吧，x=sin²a, y=cos²b∴ x²/y+(1-x)²/(1-y)=1∴ x²(1-y)+(1-x)²y=y(1-y)∴ x²-x²y+y-2xy+x²y=y-y²∴ x²-2xy+y²=0∴ (x-y)²=0∴ x=y∴ sin²a=cos²b即 sina=cosb(∵a,b是銳角)∴ a+b=90°