This question belongs to greatest common factor.
Given, there are two types of trees.
25 elm trees and 20 oak trees.
Let's find the factors of 25 and 20
25 = 5 * 5
20 = 5* 4
The common factor between both the numbers is 5.
Hence, there should be 5 areas so that the trees can be planted equally.
Answer = 5 areas.
Sin² x + sin x cos x = 0
sin x ( sin x + cos x ) = 0
sin x = 0 ; x 1 = k π ; k ∈ Z
sin x + cos x = 0 / ²
sin² x + 2 sin x cos x + cos² x = 0
2 sin x cos x + 1 =0
sin ( 2 x ) = - 1
x = 3π / 2 + 2 kπ / : 2
x 2 = 3π / 4 + kπ ; k ∈ Z