SOLUTION: I am a little confused on how to solve this. I need to solve and give exact and approximate solution to three decimal places. Any help, showing steps, would be really appreciate

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: I am a little confused on how to solve this. I need to solve and give exact and approximate solution to three decimal places. Any help, showing steps, would be really appreciate      Log On


   



Question 634449: I am a little confused on how to solve this. I need to solve and give exact and approximate solution to three decimal places. Any help, showing steps, would be really appreciated so I can understand how to do this type of problem. THanks.
y^2-18y+81=25

Found 2 solutions by ankor@dixie-net.com, josmiceli:
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
y^2 - 18y + 81 = 25
subtract 25 from both sides and solve it as a quadratic equation
y^2 - 18y + 81 - 25 = 0
y^2 - 18y + 56 = 0
You can use the quadratic formula, but this will factor to
(y-4)(y-14) = 0
Two solutions which are integers
y = 4
and
y = 14

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+y%5E2+-+18y+%2B+81+=+25+
+y%5E2+-+18y+=+-56+
Complete the square
+y%5E2+-+18y+%2B+%2818%2F2%29%5E2+=+-56+%2B+%2818%2F2%29%5E2+
+y%5E2+-+18y+%2B+81+=+-56+%2B+81+
This ends up being what I started with,
since I didn't realize both sides were
perfect squares, but now I've proven it
+%28+y+-+9+%29%5E2++=+5%5E2+
Take the square root of both sides
+y+-+9+=+5+
+y+=+14+
and taking negative square root of +5%5E2+
+y+-+9+=+-5+
+y+=+4+
I can check by plugging both results back into equation
+y%5E2+-+18y+%2B+81+=+25+
+14%5E2+-+18%2A14+%2B+81+=+25+
+196+-+252+%2B+81+=+25+
+25+=+25+
and
+4%5E2+-+18%2A4+%2B+81+=+25+
+16+-+72+%2B+81+=+25+
+25+=+25+
OK