Step-by-step explanation:
Given : A triangle with side lengths 
To find : Prove that when x > 1, it is a right triangle. Use the Pythagorean theorem and the given side lengths to create an equation. Use the equation to show that this triangle follows the rule describing right triangles. Explain your steps ?
Solution :
For right triangle the Pythagorean theorem is to be satisfied.
i.e. 
Here,
Substitute the values,
LHS=RHS
It is a right triangle.
As we know the formula to calculate the line of equation is y - y1 = m (x - x1)
Where m is the slope. y1 is the first y co ordinate. x1 is the first x co ordinate.
Now we do know that the slope of parallel line is the same as the slope of the original line.
So parallel line slope is 3 so slope for our line is 3. Hence equation is y - 7 = 3 (x - 2) which becomes y = 3x + 1.
F(d)=(d+1)(d-1+6)
f(d)=(d+1)(d+5)
f(2)=(2+1)(2+5)
f(2)=(3)(7)
f(2)=21
The answer is y=x-4
......................................
All you have to do is multiply both
