A calculus problem by Parth Lohomi

Calculus Level 1

What is the slope of the line tangent to the parabola shown in the figure above?


The answer is 2.

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4 solutions

Chew-Seong Cheong
May 25, 2016

We note that the line (red) tangent to the parabola cuts the x x -axis and y y -axis at ( x 1 , y 1 ) = ( 1 2 , 0 ) (x_1, y_1) = \left(\frac{1}{2}, 0\right) and ( x 2 , y 2 ) = ( 0 , 1 ) (x_2, y_2) = (0,-1) respectively. The gradient m m of the line is given by:

m = y 2 y 1 x 2 x 1 = 1 0 0 1 2 = 2 \begin{aligned} m & = \frac{y_2-y_1}{x_2-x_1} = \frac{-1-0}{0-\frac12} = \boxed{2} \end{aligned}

It can be seen that the parabola is y = x 2 y = x^2 . Therefore its gradient at x x is given by d y d x = 2 x \dfrac {dy}{dx} = 2x . Since the tangent touches the parabola at x = 1 x=1 , therefore the gradient is 2 \boxed{2} .

this is wrong answer y=x^2 and y'=2x y=mx+c through pass point (0,1) c=-1 and now touching point line and curve we have this equation x^2=2x*x-1then x=+ 1 and -1 and slope of tangent +2 or -2

Mohammed Rahimzadeh - 4 years, 11 months ago

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The tangent shown in the figure has a slope of 2.

Chew-Seong Cheong - 4 years, 10 months ago

It is clear that the line can't have a negative slope Mohammed

Peter van der Linden - 4 years, 10 months ago

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IN this case(figure​) yes but negative answer is acceptable .

Mohammed Rahimzadeh - 4 years, 10 months ago

It is clear that the line can't have a negative slope @Mohammed Rahimzadeh

Peter van der Linden - 4 years, 10 months ago

Wrong answer n wrong assumption s

Prince Dawra - 4 years, 9 months ago

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Too many assumptions in this problem. The curve could be y=x^2 and the line does not necessarily cross at (0,-1). Since when do math problems rely on what is seen in a picture?

Ray C - 4 years, 8 months ago

actually you shouldn't take 0, and ½ though it's right, because that's not made clear. in fact solution to go thus : [1 - (-1)] ÷ [0 - (- 1)]

Rayyan -1 - 8 months, 1 week ago
Calin Jula
Apr 14, 2017

We can see that the blue graph represents f ( x ) = x 2 f(x)=x^2 . The slope of the tangent line is f ( x 0 ) f'(x_0) where x 0 x_0 is the point where the line is tangent. We can see that x 0 = 1 x_0=1 so f ( x ) = 2 x = > f ( 1 ) = 2 f'(x)=2*x => f'(1)=2 so the correct answer is 2.

Omkar Bhabal
Sep 9, 2017

we can use the equation y=mx+c to find the slope here the red line cuts y- axis at (0,-1) therefore,c = -1 & the line touches the point (1,1) so x=1 & y=1 y=mx+c (1)=m(1)+(-1) 1=m -1 hence, m=2

Mx+4%1=4.3424454545

Simon Walden - 1 year, 7 months ago
Raymond Fang
Jan 25, 2021

We have: { y = m x 1 y = x 2 \begin{cases}y=mx-1\\y=x^2\\ \end{cases} so m x 1 = x 2 x 2 m x + 1 = 0 mx-1=x^2 \newline x^2 - mx + 1 = 0 \newline Here x has only one solution so Δ = 0 b 2 4 a c = 0 m 2 4 = 0 m 2 = 4 \Delta = 0 \newline b^2-4ac=0 \newline m^2-4=0 \newline m^2 = 4 \newline m must be greater than 0 so m = 2 . m = \boxed{2}.

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