How do you solve #5 - x^2 = 20#? Algebra Quadratic Equations and Functions Comparing Methods for Solving Quadratics 1 Answer Dan Kemp Jun 1, 2017 #x = -3.873# Explanation: #5-x^2 = 20# #-x^2 = 20-5# #-x^2 = 15# #-x = sqrt15# #-x = 3.873# #color(blue)(x = -3.873# We can now prove our answer by substituting #x# for #-3.873# #5-x^2 = 20# #5- -3.873^2 = 20# #5 + 3.873^2 = 20# #5 + 15 = 20# Answer link Related questions What are the different methods for solving quadratic equations? What would be the best method to solve #-3x^2+12x+1=0#? How do you solve #-4x^2+4x=9#? What are the two numbers if the product of two consecutive integers is 72? Which method do you use to solve the quadratic equation #81x^2+1=0#? How do you solve #-4x^2+4000x=0#? How do you solve for x in #x^2-6x+4=0#? How do you solve #x^2-6x-16=0# by factoring? How do you solve by factoring and using the principle of zero products #x^2 + 7x + 6 = 0#? How do you solve #x^2=2x#? See all questions in Comparing Methods for Solving Quadratics Impact of this question 2413 views around the world You can reuse this answer Creative Commons License