Đáp án+Giải thích các bước giải:
1/ tính nhanh
`a) (143 - 863 ) - ( - 37 + 143 ) `
`= 143 - 863 + 37 - 143`
`= (143 - 143)+(-863+37)`
`= 0 + (-826)`
`= -826`
2/ Thực hiện phép tính
`a) 5.4^2 - 18 : 3^2`
`= 5 . 16 - 18 : 9`
`= 80 - 2`
`= 78`
`b) 80 - [ 130 - ( 12- 4 )^2 ]`
`= 80 - (130 - 8^2)`
`= 80 - (130 - 64)`
`= 80 - 66`
`= 14`
3/ Tìm x , biết :
`a) x- 4^2 = 5^2`
`→ x - 16 = 25`
`→ x = 25 + 16`
`→ x = 41`
`b) x - 3/5 = 4/5`
`→ x = 4/5 + 3/5`
`→ x = {4+3}/5`
`→ x = 7/5`
`c) ( 4,5 - 2x ) . 1 4/7 = 11/4`
`→ (4,5 - 2x) . 11/7 = 11/4`
`→ 4,5 - 2x = 11/4 : 11/7`
`→ 9/2 - 2x = 11/4 . 7/11`
`→ 9/2 - 2x = {11.7}/{4.11}`
`→ 9/2 - 2x = 7/4`
`→ -2x = 7/4 - 9/2`
`→ -2x = 7/4 - 18/4`
`→ -2x = {7-18}/4`
`→ -2x = -11/4`
`→ x = -11/4 : (-2)`
`→ x = -11/4 . (-1/2)`
`→ x = {-11.(-1)}/4.2`
`→ x = 11/8`
