(ac−an)x−(bm+cn)y+(a+3c)z. (mn−1)x−(mn+1)y+(mn+1)z. [2]Exercise21. x2+7x. 8x2−12xy. 14xy−21y2. 2ax−4a2. bx−3b2. −6a3+9a2b. 10x2z+15xz2. 5a3b−25a2b2. −x2y2+3xy3. 4x5−6x4. 4x2y−12y3. −x4+3x2y2. −a3b3+a5b2. a4b2+a5. 4x5−6x4+2x3. 5a3b−25a2b2−5ab3. a5+2a4b+2a3b2. a3b3+2a2b4+2ab5. 8x3−12x2y−18xy2. x2y+2xy2−y3. a5+a4b2+a2b3. x2y2−2xy3+y4. 15a4b4−20a3b5+5a5b3.