$x_1+x_2+x_3 = 6$
$y_1+y_2+y_3 = 21$
$x_1^2+x_2^2+x_3^2 =14$
$x_1y_1+x_2y_2+x_3y_3 = 46$
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we have equation of line ,$y=a+bx$, to which $(x_1,y_1),(x_2,y_2)\quad and \quad (x_3,y_3)$ satisfies
$y_1=a+bx_1$ ,
$y_2=a+bx_2$, and
$y_3=a+bx_3$
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from these equations we get ,
$y_1+y_2+y_3=3a+b(x_1+x_2+x_3)$
$21= 3a +6b$ ______$eq(1)$
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$x_1y_1 = ax_1+bx_1^2$
$x_2y_2 = ax_2+bx_2^2$
$x_3y_3 = ax_3+bx_3^2$
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from these equations we get
$x_1y_1+x_2y_2+x_3y_3 = a(x_1+x_2+x_3)+b(x_1^2+x_2^2+x_3^2)$
$46 = 6a+14b$ ______$eq(2)$
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so from equation $(1)$ and $(2)$
we get $a= 3$ and $b=2$