How do you solve the system #x^2+y^2=25# and #y=-3#? Precalculus Solving Systems of Two Equations Solving by Substitution 1 Answer Alan P. Dec 9, 2016 #color(green)((x,y)=(-4,-3))# and #color(green)((x,y)=(+4,-3))# Explanation: If #color(blue)x^2+color(red)y^2=25# and #color(red)y=color(red)(-3)# then #color(white)("XXX")color(blue)x^2+(color(red)(-3))^2=25# #color(white)("XXX")color(blue)x^2+9=25# #color(white)("XXX")color(blue)x^2=16# #color(white)("XXX")color(blue)x=+-4# Answer link Related questions What is a system of equations? What does it mean to solve a system of equations by substitution? How do I use substitution to find the solution of the system of equations #c+3d=8# and #c=4d-6#? How do you write a system of linear equations in two variables? How does a system of linear equations have no solution? How many solutions can a system of linear equations have? What is the final step of completing a solve by substitution problem? How do I use substitution to find the solution of the system of equations #4x+3y=7# and #3x+5y=8#? How do I use substitution to find the solution of the system of equations #y=2x+1# and #2y=4x+2#? How do I use substitution to find the solution of the system of equations #y=1/3x+7/3# and... See all questions in Solving by Substitution Impact of this question 3025 views around the world You can reuse this answer Creative Commons License