先化简后求值:(3a-4b)^2-3a(3a-4b)/-3b,其中a=-1,b=3.
问题描述：
先化简后求值:(3a-4b)^2-3a(3a-4b)/-3b,其中a=-1,b=3.
rt
答
是：(3a-4b)²-3a(3a-4b)/(-3b)?
还是：[(3a-4b)²-3a(3a-4b)]/(-3b)?
如果是：(3a-4b)²-3a(3a-4b)/(-3b)
(3a-4b)²-3a(3a-4b)/(-3b)
=(3a-4b)²+3a(3a-4b)/(3b)
=(3a-4b)[(3a-4b)+3a/(3b)]
=(3a-4b)(3a-4b+a/b)
=(3a-4b)(3ab-4b²+a)/b
=[3×(-1)-4×3][3×(-1)×3-4×3²+(-1)]/3
=(-15)×(-46)/3
=5×46
=230
如果是[(3a-4b)²-3a(3a-4b)]/(-3b)
[(3a-4b)²-3a(3a-4b)]/(-3b)
=(3a-4b)[(3a-4b)-3a]/(-3b)
=(3a-4b)(-4b)/(-3b)
=(3a-4b)(4/3)
=[3×(-1)-4×3](4/3)
=(-3-12)×4/3
=[(-15)/3]×4
=-20