Practicing Success
If the line y = 2x touches the curve $y=ax^2+bx+c$ at the point where x = 1 and the curve passes through the point (-1, 0), then |
$a=\frac{1}{2}, b=1, c=\frac{1}{2}$ $a=1, b=\frac{1}{2}, c=\frac{1}{2}$ $a=\frac{1}{2}, c=\frac{1}{2}, b=1$ none of these |
$a=\frac{1}{2}, b=1, c=\frac{1}{2}$ |
We have, $y=a x^2+b x+c$ ........(i) $\Rightarrow \frac{d y}{d x}=2 a x+b \Rightarrow\left(\frac{d y}{d x}\right)_{x=1}=2 a+b$ Since, the line y = 2x touches (i) at the point where x = 1. ∴ (Slope of the tangent at x = 1) = (Slope of the line y = 2x) $\Rightarrow 2 a+b=2$ ........(ii) Putting x = 1 in y = 2x, we get y = 2 Thus the given line touches the curve (i) at (1, 2) Clearly, (1, 2) and (-1, 0) lie on (i). Therefore, $2=a+b+c$ ...(iii) and, $0=a-b+c$ .......(iv) Solving (i), (ii) and (iii), we get $a=\frac{1}{2}, b=1$ and $c=\frac{1}{2}$ |