计数:(-2/5)²÷(-12/5)-8/21×(-7/4)-0.25
问题描述:
计数:(-2/5)²÷(-12/5)-8/21×(-7/4)-0.25
计数:(1)(-2/5)²÷(-12/5)-8/21×(-7/4)-0.25 (2)(-2)³-2²-(-3)³+3²
(3)先化简,在求值:5a²-[a²-(2a-5a²)-2(a²-3a)],a=4
答
(1)(-2/5)²÷(-12/5)-8/21×(-7/4)-0.25
=(4/25)(-5/12)+2/3-1/4
= -1/15+2/3-1/4
=7/20
(2)(-2)³-2²-(-3)³+3²
=-8-4+27+9=24
(3)先化简,在求值:5a²-[a²-(2a-5a²)-2(a²-3a)],a=4
=5a²-a²+2a-5a²+2a²-6a=5a²-4a=64