先化简,再求值:[(3a-7)²-(a+5)²]/(4a-24),其中a=1/50

先化简,再求值:[(3a-7)²-(a+5)²]/(4a-24),其中a=1/50
先化简,再求值:[(3a-7)²-(a+5)²]/(4a-24),其中a=1/50

先化简,再求值:[(3a-7)²-(a+5)²]/(4a-24),其中a=1/50
[(3a-7)^2-(a+5)^2]/(4a-24)
=[(9a²-42a+49)-(a²+10a+25)]/(4a-24)
=(8a²-52a+24)/[4(a-6)]
=(a-6)(8a-4)/[4(a-6)]
=(8a-4)/4
=2a-1
=2*(1/50)-1
=1/25-1
=-24/25

[(3a-7)²-(a+5)²]/(4a-24)
=[3a-7+(a+5)][3a-7-(a+5)]/(4a-24)-------平方差公式
=[4a-2][2a-12]/4(a-6)
=4(2a-1)*2(a-6)/4(a-6)--------提公因式
=2a-1--------约分
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