3с^2* (5с-8)=15c^3-24c^2
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bn = b1*q^(n-1)
b5 = b1*q^4 = (-125)* 0,2^4 = (-125) * 0,0016 = - 0,2
1+ tg ^2 x = 1/ cos^2 x
1+7 = 1/ 50cos^ x
8= 1/ 50 cos^ x
8* 50 cos^2 x =1
400 cos^ x =1
cos^2 x = 1/400
cosx =1/20
cos x = 0.05
Наверное так:
6 в степени 2n+4 /37