Giải bài 7.28 trang 38 toán 7 tập 2 kết nối tri thức.
a) (5x3–2x2+4x–4)(x3+3x2–5)
=5x3.x3+5x3.3x2+5x3.(−5)+(–2x2).x3+(–2x2).(–2x2)+(–2x2).(−5)
+4x.x3+4x.3x2+4x.(−5)+(−4).x3+(−4).3x2+(−4).(−5)
=5x6+15x5–25x3–2x5+4x4+10x2+4x4+12x3–20x−4x3–12x2+20
=5x6+13x5–2x4–17x3–2x2–20x+20
b) (−2,5x4+0,5x2+1) và (4x3–2x+6)
=(−2,5x4).4x3+(−2,5x4).(−2x)+(−2,5x4).6+0,5x2.4x3+0,5x2.(−2x)
+0,5x2.6+4x3–2x+6
=−10x7+5x5–15x4+2x5−x3+3x2+4x3–2x+6
=−10x7+7x5–15x4+3x3+3x2–2x+6
