Known expression: h (t) =-5t2+120t+m.

At t= 10, a rocket was launched from a platform m meters above the ground. Before the rocket reaches the ground, the expression of its height h, which is about t from the ground, has been given on the rod in meters.

Q: At what moment is the height of the rocket the same as that at t= 10?

A 8

B 12

C 14

D 16

E 18

explain

Step 1: Find the symmetry axis of the quadratic function =-b/2a =-120/-10 =12.

So the image is symmetrical about t= 12.

Step 2: Find the symmetry point X of t= 10 about t= 12.

(x+ 10)/2= 12

x+ 10=24

x= 14

Therefore, when t= 14, it has the same h as t= 10, that is, the same height.

Choose C.

The second method: you can also find the unknown H in the era of t= 10, and then find the second T. ..