2.1*2.1+c*c=13.1*13.1

Solution for 2.1*2.1+c*c=13.1*13.1 equation:

Simplifying
2.1 * 2.1 + c * c = 13.1 * 13.1

Multiply 2.1 * 2.1
4.41 + c * c = 13.1 * 13.1

Multiply c * c
4.41 + c2 = 13.1 * 13.1

Multiply 13.1 * 13.1
4.41 + c2 = 171.61

Solving
4.41 + c2 = 171.61

Solving for variable 'c'.

Move all terms containing c to the left, all other terms to the right.

Add '-4.41' to each side of the equation.
4.41 + -4.41 + c2 = 171.61 + -4.41

Combine like terms: 4.41 + -4.41 = 0.00
0.00 + c2 = 171.61 + -4.41
c2 = 171.61 + -4.41

Combine like terms: 171.61 + -4.41 = 167.2
c2 = 167.2

Simplifying
c2 = 167.2

Take the square root of each side:
c = {-12.9305839, 12.9305839}