Bài 1 trang 17 SGK Toán 8 Chân trời sáng tạo Tập 1 - KNTT

a) Ta có: x + 2y + (x – y)

= x + 2y + x – y

= (x + x) + (2y – y)

= 2x + y.

b) Ta có: 2x – y – (3x – 5y)

= 2x – y – 3x + 5y

= (2x – 3x) + (–y + 5y)

= –x + 4y.

c) Ta có: 3x² – 4y² + 6xy + 7 + (–x² + y² – 8xy + 9x + 1)

= 3x² – 4y² + 6xy + 7 – x² + y² – 8xy + 9x + 1

= (3x² – x²) + (– 4y² + y²) + (6xy – 8xy) + 9x + (7 + 1)

= 2x² – 3y² – 2xy + 9x + 8 .

d) Ta có: 4x²y – 2xy² + 8 – (3x²y + 9xy² – 12xy + 6).

= 4x²y – 2xy² + 8 – 3x²y – 9xy² + 12xy – 6

= (4x²y – 3x²y) + (– 2xy² – 9xy²) + 12xy + (8 – 6)

= x²y – 11xy² + 12xy + 2 .

-- Mod Toán 8 HỌC247