( X - 5 )*( X - 3 ) = 0
X^2 - 3X - 5X + 15 = 0
X^2 - 8X + 15 = 0
1)2ab+a
2)5x^2-6-2xy-6x/x
3)-b-9/2-2a
5)5b^2+3a^2/18ab
6)2x^2-9y^2/48xy
1. (1 - cos^2t / 1-sin^2t) + tgt*ctgt = 1 / cos^2t
sin^2t / cos^2t + 1 = (sin^2t + cos^2t) / cos^2t = 1 / cos^2t
1/cos^2t = 1/cos^2t
2. sint = -15/17
cos^2t = 1 - sin^2t = 1 - 225/289 = 64/289
cost = -8/17
tgt = sint/cost
tgt = 15*17/17*8 = 15/8
ctgt = 1/tgt = 8/15
5^2n*2^n / 5^2n-1 * 2^n-1 = 5*2=10