Answer: I used the Pythagorean theorem and got 6.24, but if I was supposed to use another method, just let me know.
The formula is a^2+b^2=c^2
a=5
c=8
b=?
5^2+b^2=8^2
25+b^2=64
b^2=39
b=6.24,
(If it doesn't work, put x=6.24, x=-6.24. It can be both technically, but most teachers ask only for the first one. )
(4x+5)(4x-5) is equal to 16x^2+20x-20x-25
The positive and negative 20x cancel out
Leaving you with: 16x^2 - 25
[S/N this is a pattern that shows up a decent amount. Whenever you have something that looks like (x^2-y^2) it factors out to (x+y)(x-y). It might be helpful to remember]
The next one, (4x+5)2, just follows the distributive property. Multiply both components within the parentheses bye the coefficient of 2: 8x+10
IF you mean

, then the following would be a solution:
First add 16 to both sides of the equation:

Now divide both sides of the equation by 3:

Take the square root of both sides to solve for "X", or simply solve by inspection: "what number(s) can be squared to get 49?"
Answer: -7 and 7 So the smallest solution would be "-7"
Answer: x = 3π/2
Hope this helps...... Stay safe and have a great rest of the weekend!!! :D