The square of 2a+the square of 3b = 10, (2)

Add the formula (1) to the formula (2) to obtain

(3a squared -4b squared) +(2a squared +3b squared) =5+ 10.

Simplification: the square of 5a-the square of b = 15, and both sides are multiplied by -3.

-15a squared +3b squared =-45.

2. (Analysis: Because the playground is round, A is in front of B 100 meters, which can also be regarded as B is 300 meters in front of A. When A meets B, A can be regarded as catching up with B, that is, A runs 300 meters more than B.)

Solution: Let A and B meet after X minutes, then 100x-80x=300.

The solution is x= 15.

A: Party A and Party B will meet in 15 minutes.

3. Solution: Suppose Xiao Gang spent x seconds in the sprint, then he spent (65-x) seconds before the sprint.

6(65-x)+8x=400

To solve this equation, x=5.

A: Xiao Gang spent five seconds in the sprint.