20a²-45b²=5·(4a²-9b²)=5·(2a-3b)·(2a+3b)
<span> 1/sina-1 - 1/sina+1=(sina+1-sina+1)/(sina-1)(sina+1)=2/(sin</span>²a<span>-1)=-2/cos</span>²a
(5x - 1)^2 - 16x^2 = 0
(5x - 1 - 4x)(5x - 1 + 4x) = 0
(x - 1)(9x - 1) = 0
x - 1 = 0
x = 1
9x - 1 = 0
9x = 1
x = 1/9
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x^2 + 6x + 9 + x^2 - 8x + 16 = 2(4x + 12 - x^2 - 3x)
2x^2 - 2x + 25 = 2(x + 12 - x^2)
2x^2 - 2x + 25 = 2x + 24 - 2x^2
4x^2 - 4x + 1 = 0
(2x - 1)^2 = 0
2x - 1 = 0
2x = 1
x = 1/2 = 0,5
3/9 наверно. это не точно сори
1)5sinx-3+5cosx=5(sinx+cosx)-3=5(sinx+sin(π/2-x))-3=5*2sinπ/4 cos(x-π/4)-3=
=5√2cos(x-π/4)-3
2)7sinx-5+7cosx=7√2cos(x-π/4)-5
3)1-sinx ctgx cosx=1-sinx*(cosx/sinx)*cosx=1-cos²x=sin²x
4) (cos²x-sin²x) / (2cos²x-1) = cos2x / cos2x =1
5) (cos2a+1)tg²a-1=2cos²a*(sin²a / cos²a)-1=2sin²a-1= -cos2a
6)(sina+cosa)²-1=sin²a+2sina cosa+cos²a-1=2sina cosa=sin2a