( 1)7+8= 15

7+8+2= 15+(2)

7+8- 10= 15-( 10)

Add fire to both sides of the equation, subtract the same number, and the equation remains the same.

(2)9+7= 16

(9+7) divided by 2= 16 divided by 2

(9+7) times 3= 16 times 3.

Both sides of the equation are multiplied or divided by the same number at the same time (except 0), and the equation remains unchanged.

Second,

(1)7X=28 (X=3 X=4) The second one is correct.

(2) 18+X=23 (X=4 X=5) The second one is correct.

Third,

Right, right and wrong

outdoor training

1 、( 3)3n(2X)

2、(3) (2) (3)