(x-5)²=(x-8)²
x² - 10x + 25 = x² - 16x + 64
6x = 39
x= 6,5
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(-x-5)*(2x+4)=0
-x-5 = 0
x₁= -5
2x+4=0
x₂= -2
1) sin^4α+cos²α+sin²αcos²α=sin^4α+sin²αcos²α+cos²α=sin²α(sin²α+cos²α)+cos²α=sin²α+cos²α=1;
2) sin^4α-cos^4α-sin²α+cos²α=(sin²α-cos²α)(sin²α+cos²α)-sin²α+cos²α=sin²α-cos²α-sin²α+cos²α=0;
3) cos²α/(1-sin²α)=cos²α/cos²α=1;
4) (1-2sin²α)/(2cos²α-1)=(sin²α+cos²α-2sin²α)/(2cos²α-sin²α-cos²α)=(cos²α-sin²α)/(cos²α-sin²α)=1.
Прогрессия (an) , если a6= 72 , d=-2 = 174