數學題目!急用!請進!

s=厂(u^2-2gh)
s^2=u^2-2gh
2gh=u^2-s^2
g=(u^2-s^2)/2h
2
(3^-m)x(9^m+n)∕3^(m+n)
=(3^-m)x(3^2(m+n))∕3^(m+n)
=3^(-m+2m+2n-m-n)
=3^n
3(a)
a^2-5ab+6b^2
=(a-2b)(a-3b)
(b)
x^2-5xy+6y^2+x-2y
=(x-2y)(x-3y)+(x-2y)
=(x-2y)(x-3y+1)
4 一箱內盛有(2n+2)個黃色、2n個藍色和(3n-1)個綠色的球。自箱中隨機取出一球,若該球為黃色的概率是2∕5,求n的值。
自箱中隨機取出一球為黃球概率
=(2n+2)/(2n+2+2n+3n-1)
=(2n+2)/(7n+1)
令(2n+2)/(7n+1)=2/5
5(2n+2)=2(7n+1)
10n+10=14n+2
8=4n
n=2

第一題的題目係 u = √(u^2-2gh)?

The answer of question 4
n=1/2