Giải câu 4 trang 54 sách toán VNEN lớp 7 tập 2.
P + Q + H = (2x4 – x – 2x3 + 1) + (5x2 – x3 + 4x) + (- 2x4 + x2 + 5)
= 2x4 – x – 2x3 + 1 + 5x2 – x3 + 4x – 2x4 + x2 + 5
= (2x4 – 2x4) – (2x3 + x3) + (5x2 + x2) + (4x – x) + (1 + 5)
= – 3x3 + 6x2 + 3x + 6
P – Q – H = (2x4 – x – 2x3 + 1) – (5x2 – x3 + 4x) – (- 2x4 + x2 + 5)
= 2x4 – x – 2x3 + 1 – 5x2 + x3 – 4x + 2x4 – x2 – 5
= (2x4 + 2x4) – (2x3 – x3) – (5x2 + x2) – (4x + x) + (1 – 5)
= 4x4 – x3 – 6x2 + 5x – 4