How do I graph 9x^2+16y^2-36x+32y=929x2+16y236x+32y=92 algebraically?

1 Answer
Oct 19, 2014

By grouping xx's and yy's together,

Rightarrow (9x^2-36x)+(16y^2+32y)=92(9x236x)+(16y2+32y)=92

by factoring out 9 and 16,

Rightarrow9(x^2-4x)+16(y^2+2y)=929(x24x)+16(y2+2y)=92

by adding and subtracting 4 and 1 in the parentheses,

Rightarrow9(x^2-4x+4-4)+16(y^2+2y+1-1)=929(x24x+44)+16(y2+2y+11)=92

by keeping the first three terms in each group,

Rightarrow9(x^2-4x+4)-36+16(y^2+2y+1)-16=929(x24x+4)36+16(y2+2y+1)16=92

by completing the squares and adding 36 and 16,

Rightarrow9(x-2)^2+16(y+1)^2=1449(x2)2+16(y+1)2=144

by dividing by 144,

Rightarrow(x-2)^2/{16}+(y+1)^2/{9}=1(x2)216+(y+1)29=1

Hence, we have an equation of an ellipse

(x-2)^2/{4^2}+(y+1)^2/{3^2}=1(x2)242+(y+1)232=1,

which is 8 units wide, 6 units tall, and centered at (2,-1)(2,1).

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I hope that this was helpful.