Question #293446

The equation of a circle is given by 2x^2+2y^2-8x+5y-10=0 find the coordinates of P and Q if the circle cuts the x-axis as at the points P and Q

1
Expert's answer
2022-02-04T05:28:20-0500

Equation of the circle is, 2x2+2y28x+5y10=02x^2+2y^2-8x+5y-10=0. We first write this equation in the form, (xh)2+(yk)2=r2(x - h)^ 2 + (y - k) ^2 = r ^2 where (h,k)(h,k) and rr are the center and radius of the circle.

So,

2x2+2y28x+5y10=0    2x2+2y28x+5y=102x^2+2y^2-8x+5y-10=0\implies 2x^2+2y^2-8x+5y=10. Putting the xx terms and yy terms together,

2x28x+2y2+5y=102x^2-8x+2y^2+5y=10

Dividing through by 2,

x24x+y2+52y=5x^2-4x+y^2+{5\over2}y=5

Completing the squares,

(x24x+4)+(y2+52y+2516)=5+4+2516=16916(x^2-4x+4)+(y^2+{5\over2}y+{25\over16})=5+4+{25\over16}={169\over16}

We can rewrite this equation as,

(x2)2+(y+54)2=16916...........(1)(x-2)^2+(y+{5\over4})^2={169\over16}...........(1).This is the equation of the circle.

The center of this circle has coordinates (2,54)(2,-{5\over 4}) and radius r=134r={13\over4}


To find the xx intercept, we set y=0y=0 in equation 1.

Setting y=0y=0 in equation 1,

(x2)2+(54)2=16916    (x2)2=14416    x2=±14416(x-2)^2+({5\over4})^2={169\over16}\implies (x-2)^2={144\over16}\implies x-2=\pm\sqrt{144\over16}

The values of xx when y=0y=0 are therefore,

x2=±14416    x=2±3x-2=\pm\sqrt{144\over16}\implies x=2\pm3

Therefore,

x=1,5x=-1,5

Thus, the xx intercepts are, P=(1,0)P=(-1,0) and Q=(5,0)Q=(5,0)


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