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)
=(4a-2)(2a-12)/(4a - 24)
=2a-1
=2/50-1
=-24/25

[(3a - 7)² - (a+5)² ] /(4a - 24),
=(3a-7+a+5)(3a-7-a-5)/4(a-6)
=(4a-2)(2a-12)4(a-6)
=4(2a-1)(a-6)/4(a-6)
=2a-1 a=1/50
=2/50-1
=-24/25

[(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)/[4(a-6)]
=(4a-2)(2a-12)/[4(a-6)]
=4(2a-1)(a-6)/[4(a-6)]
=2a-1
带入 a=1/50 得
1/25-1=-24/25