Completing the square

What value of c would make this a perfect square trinomial?
x² +8x + c

x^2 + 4x + 1 = 0

Solve the quadratic equation by completing the square: x² + 12x + 8 = 0

Solve the equation by completing the square: x^2 + 6x - 4 = 36

Complete the square for $$f(x)=x^2-4x-12$$ and leave in vertex form.

Complete the square for the equation $$f\left(x\right)=2x^2-12x+24$$ and leave in vertex form.

Complete the square for the equation $$x^2+8x-67=-2$$ and leave in vertex form.

Complete the square for $$f(x)=x^2+2x-15$$ and find the zeros.

Complete the square for $$f(x)=x^2-16x+43$$ and find the zeros.

Complete the square and find the zeros for $$f(x)=2x^2-20x+10$$