x2+7x−30. x2−7x−30. a2+ab−6b2. a2−ab−6b2. a2+3ab−4b2. a2−3ab−4b2. a2x2−2ax−63. a2+2ax−63x2. a2−9ab+20b2. x2y2−19xyz+48z2. a2b2+15abc+44c2. x2−13xy+36y2. x2+19xy+84y2. a2x2−23axy+102y2. x4−9x2y2+20y4. a4x4−24a2x2y2+143y4. a6b6−23a3b3c2+132c4. a2−20abc−96b2c2. a2−4abc−96b2c2. a2−10abc−96b2c2. a2+29abc−96b2c2. a2−46abc−96b2c2. a2+49abc+48b2c2. x2−18xyz−243y2z2. x2y2−xyz−182z2. Exercise 39.