專題訓(xùn)練一分式化簡(jiǎn)求值的幾種類型化簡(jiǎn)后直接代入求值1.先化簡(jiǎn),再求值:x2-9x-1÷x2.先化簡(jiǎn),再求值:1+1x+1·x+13.先化簡(jiǎn),再求值:x-yx2-2xy+4.先化簡(jiǎn),再求值:x+2+3x-2÷化簡(jiǎn)后整體代入5.先化簡(jiǎn),再求值:a2b-a÷a2-b26.已知a=b+2025,求式子2a-b×a27.先化簡(jiǎn),再求值:1-2x÷x2-4x+4x2-4化簡(jiǎn)后選值代入8.先化簡(jiǎn)1-1a-1÷9.先化簡(jiǎn),再求值:x2-xx2+2x+1÷2x+1-110.先化簡(jiǎn),再求值:1-3a-10a-211.有一道題:“先化簡(jiǎn):3x2+9xx2+6x+9小倩同學(xué)的解答過(guò)程是:解:原式=3x(x+3)(x+3)2·x當(dāng)x=0時(shí),原式=3×0+9=9.作業(yè)發(fā)下來(lái)后,小倩發(fā)現(xiàn)老師在求值的結(jié)果上畫(huà)了個(gè)大問(wèn)號(hào),她百思不得其解,你能幫小倩同學(xué)找到問(wèn)題出在哪里嗎?設(shè)參法化簡(jiǎn)求值12.已知x2=y3=z4≠0,求

【詳解答案】1.解:原式=(x-3)(x+3)x-1·當(dāng)x=2時(shí),原式=322.解:原式=x+1x+1+1x+1·x當(dāng)x=3時(shí),原式=13-23.解:原式=x-y(x-y)2-xx(x-2y)當(dāng)x=3,y=1時(shí),原式=-13-14.解:原式=(x+2)(x-2)x-當(dāng)x=2025時(shí),原式=2025-125.解:a2b=a2-=a(a=aa當(dāng)a=2b時(shí),原式=2b2b+b6.解:原式=2a-b·(a+b)(a-b當(dāng)a=b+2025時(shí),原式=2(b+2025-b)=4050.7.解:原式=x-2x·=x+2x=(=4x∵x2+2x-15=0,∴x2+2x=15,∴原式=4158.解:原式=a-2a-=a-2a-=2a-=3a∵a=1,2時(shí)分式無(wú)意義,∴a=3.當(dāng)a=3時(shí),原式=329.解:原式=x(x-1)(x+1)由題意,可知x≠-1,x≠0,x≠1,∴當(dāng)x=2時(shí),原式=4310.解:原式=a-2-3a+10a-2·(a-2)∵a與2,3構(gòu)成三角形的三邊,∴3-2<a<3+2.∴1<a<5.∵a為整數(shù),∴a=2,3或4.又∵a-2≠0,a-4≠0,∴a≠2且a≠4.∴a=3.∴原式=-2×3+4=-6+4=-2.11.解:化簡(jiǎn)的過(guò)程沒(méi)問(wèn)題,只是x不能取0,因?yàn)榉帜覆荒転?,當(dāng)x取0時(shí),原式就沒(méi)有意義了.故小倩同學(xué)的結(jié)果是錯(cuò)誤的.這里x也不