<span><em>Решение:
</em></span>
<u><span>cosa=√(1-cos²a)=√(1-21/25)=√(4/25)=0,4</span></u>
√ ( 18X^2 - 9 ) = X^2 - 4
( √ 18X^2 - 9 ) = ( X^2 - 4)^2
18X^2 - 9 = X^4 - 8X^2 + 16
X^4 - 8X^2 - 18X^2 + 16 + 9 = 0
X^4 - 26X^2 + 25 = 0
X^2 = A ; A > 0
A^2 - 26A + 25 = 0
D = 676 - 100 = 576 ; √ D = 24
A1 = ( 26 + 24 ) : 2 = 25 ; > 0
A2 = ( 26 - 24 ) : 2 = 1 ; > 0
X^2 = 25
X = 5 ; X = - 5
X^2 = 1
X = 1 ; X = - 1
Ответ 5 ; - 5 ; 1 ; - 1
ах = - 3х + 2
ах + 3х = 2
х( а + 3 ) = 2
а + 3 = 2 : Х
а = ( 2 / Х ) - 3
а = ( 2 - 3х ) / Х
Х не равен нулю