( a + 1 )( a - 1 ) = a^2 - 1
( a^2 - 1 )( a^2 + 1 ) = a^4 - 1
- ( 9 + a^2 )^2 = - ( 81 + 18a^2 + a^4 ) = - 81 - 18a^2 - a^4
a^4 - 1 - 81 - 18a^2 - a^4 = - 82 - 18a^2
a = 1/3
- 82 - 18*( 1/3 )^2 = - 82 - ( 18/9 ) = - 82 - 2 = - 84
Sin4x + sin2xcos2x = sin2x (sin2x + cos2x) = sin2x∙1 = sin2x
X2= 0.36
x= +,- 0.6
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4x^2-4=2(2x^2-2)
5t^2-20st+20s^2=5(t^2-4st+4s^2)
c-27cd^3=c(27d^3)
vu^3+vw^3=v(u^3+w^3)
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