The answer is 2sqrt2

Step-by-step explanation:

The triangle is isosceles. That means that the unmarked side is also x

The Pythagorean Theorem applies

x^2 + x^2 = 4^2

2x^2 = 16                 Divide by 2

2x^2/2 = 16/2

x^2 = 8

x^2 = 2 * 2 * 2

sqrt(x^2) = sqrt(2 * 2 * 2)

The rule is take one of a pair of factors out of the root sign and through the other member of the pair away. The third 2 stays under the root sign.

x = 2sqrt(2)

2x+18+5x-9

2x+5x18-9

7x+9

7. 7

x= 1.4

hope it helps