1)(sin²a-cos²a)(sin²a+cos²a)-sin²a+cos²a=sin²a-cos²a-sin²a+cos²a=0
2)cos²a/(1-sin²a)=cos²a/cos²a=1
3)(1-2sin²a)/(2cos²a-1)=cos2a/cos2a=1
6 тетрадей и 2 карандаша
(40 × 6 = 240, 15 × 2 = 30, 240 + 30 = 270.)
<span>(6/a-1) - (10/(a-1)^2) / (10/a^2-1)-(2а+2)/(а-1) =</span>
X³-15x²+75x-125+10x-15=0
x³-15x²+85x-140=0
x²(x-15)+5(17x-28)=0
(x²+5)(x-15)(17x-28)=0
корней x=15 17x=28
нет x=28/17
x=1 11/17