5) Cos = A / H
COS 50 = 6 / H
H = 6 / COS 50
H = 9.3343 m
TAN 50 = O / H
O = TAN 50 x 9.3343
O = 11.1242 m
6) 4x(x=y) - (-x-3y)^2
4x^2 + 4xy -(x^2 + 3xy + x^2 + 3xy)
4x^2 + 4xy -2x^2 +6xy
2x^2 - 2xy
7) 2mn+4n / 9-n^2 ÷ 6mn / 3-n
= 2n(m+2) / 3+n(3-n) x 3-n / 6mn
= m+2 / 3+n(3m)
8) 2t = t-1 / m-1
2t(m-1) = t-1
2mt - 2t - t = -1
t(2m-3) = -1
t = -1 / 2m-3
9) y-6 / 3 - y-4 / 2 = 1
2y-12 / 6 - 3y-12 / 6 = 1
-y = 6
y = -6
头脑生锈了