C is the answer because with this kind of math the answer can be Neg or Postive <span />
<span>x² +y² -4x -6y +8=0
(x² -4x) +(y² -6y) = -8
We are going to complete square for x and y,
it should look like a²+2ab+b² = (a +b)², or </span>a²-2ab+b² = (a -b)²,
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(x²-2*2x+2²) -2² + (y²-2*3y +3²)-3²=- 8
(x-2)²+(y-3)²-4-9=-8
</span>(x-2)²+(y-3)²=-8+13
(x-2)²+(y-3)²=5
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Formula a circle (x-h)²+(y-k)²=R², where vertex has coordinates (h, k)
So , for our circle vertex (2,3) and radius = </span>√5<span>
</span>
boy or an A student is
29 made an A + 8 boys who did not make an A
37 who made an A and/or who is a boy
37/50
Law of cosine:
c² = a² +b² -2ab*cosC.
Because the triangle is equilateral a=b=c=x,
and we can write,
x²=x² +x² -2xx*cosC
x² =2x² -2x²* cos C
-x² = -2x²*cos C
cos C= 1/2,
so m∠C=60⁰.
Because all sides are equal, and across of the equal sides should be equal angles, all angles will be also equal and = 60⁰.
