1.
s = (ah+bh)/2
2s - bh = ah
a = (2s - bh) / h
2.
1/y = (1/f1 - 1/f2)
y = 1/((f2-f1)/f1f2)
y = f1f2 / (f2-f1)
3.
a=0.(t ≠ -1)
4.
ax + 2ab = bx + a^2 + b^2
(a-b)x = a^2 - 2ab + b^2
x = (a^2 - 2ab + b^2)/(a-b)
因为
a ≠ b
所以
x = (a - b)^2 / (a - b)
= a -