Xiaoqiang did 20 calculation questions, and 3 points were deducted for one wrong question. As a result, Xiaoqiang got 60 points and asked him how many questions he did right

Xiaoqiang did 20 calculation questions, and 3 points were deducted for one wrong question. As a result, Xiaoqiang got 60 points and asked him how many questions he did right

If you do X questions right, you do (20-x) wrong
5x-3（20-x）=60
We get x = 15

A total of 20 questions, do a right question of 5 points, did not do or do a wrong question to deduct 3 points, I got 60 points is to do a few questions?

Let's do the right x, then we have the equation 5x-3 * (20-x) = 60
I got x = 15 and did 15 problems right

Solve the equation 3 ^ X - 3 ^ - x = 80 / 9

Let t = 3 ^ X
3^x - 3^-x = 80/9
t - 1/t =80/9
9t^2 - 80t - 9=0
(9t+1)(t-9)=0
T > 0
t=9
3^x=9=3^2
x=2

The area of a triangle is 56 square decimeters. One side of the triangle is 16 decimeters long. How high is the side?

Height: 56 × 2 △ 16 = 7 decimeters
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Simple operation of 0.25 times 3.2 times 4

0.25x3.2x4
=0.25x4x3.2
=1x3.2
=3.2
The use of the exchange rate of multiplication oh

It is known that AD and be are the heights of △ ABC, h is the intersection of AD and be or their extensions, BH = AC, then the degree of ∠ ABC is ()
A. 45 ° B. 135 ° C. 60 ° or 120 ° D. 45 ° or 135 ° C

There are two cases, as shown in figure (1), (2), ∵ BH = AC, ∵ BEC = ∵ ADC, ∵ ahe = ∵ Bhd, ∵ hae + ∵ C = 90 °, ∵ hae + ∵ ahe = 90 °,