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The question:

y=3.48x^2, determine the positionson the curve (x,y) of the left most tangent and the right most tangent that pass through the point (-5.67, -44.75).

If there is no tangent for either the left or right, just say none.

Round to 4 dec. places.

Thanks

math
 Aug 22, 2014

Best Answer 

 #3
avatar+26396 
+5

 

Find the most left and right tangent

y=ax2a=3.48Point (xp,yp) : (xp=5.67 , yp=44.75)Find the tanget Point (xt,yt)yt=ax2tSlop of y=ax2 is y=2axtSlop of the line through Point p is y=ytypxtxpthe slops must be equal: y=2axt=ytypxtxp2axt(xtxp)=ytyp|yt=ax2t2axt(xtxp)=ax2typ2ax2t2axtxp=ax2typ2ax2tax2t2axtxp+yp=0ax2t2axtxp+yp=0

xt1,2=xp±x2pypayt1,2=ax2t1,2

xt1=5.67+(5.67)2(44.753.48)xt1=5.67+6.70880730103=1.03880730103yt1=3.481.038807301032=3.75533971815right most tangent

xt2=5.67(5.67)2(44.753.48)xt2=5.676.70880730103=12.3788073010yt2=3.48(12.3788073010)2=533.257348282 left most tangent 

 Aug 22, 2014
 #2
avatar+130458 
+5

This one is a little tough!!

The slope of a tangent line to the given parabola at any point is just y' = 6.96x

Now, what we're looking for is at least one point on the parabola where the line through  (-5.67, - 44.75) is tangent to that point (or points).

Let's call the point(s) on the parabola (x, 3.48x^2). And the slope of the tangent line at that point is just 6.96x.

So, using this point on the parabola and the point (-5.67 , - 44.75), we have that, using the slope "formula,"

(3.48x^2 + 44.75) / (x + 5.67) = 6.96x

(3.48x^2 + 44.75)  /(x + 5.67) - 6.96x = 0

And solving this equation using the onsite calculator, we have....

(3.48×x2+44.75)(x+5.67)6.96×x=0{x=(3406662741+49329)8700x=(340666274149329)8700}{x=12.378807301025932x=1.038807301025932}

And the equation of the line that goes through (-5.67, -44.75) and touches the parabola at 1.038807301025932 is given by

 

y +44.75 = 6.96(1.038807301025932)(x + 5.67)

y = 7.23009881514048672x + 40.9946602818465597024 - 44.75

y = 7.23009881514048672x -3.7553397181534402976 ........ and rounding, we have

y = 7.23x - 3.755

 

 

And the equation of the line that touches the graph at - 12.378807301025932 is given by

y + 44.75 = 6.96( - 12.378807301025932)(x + 5.67)

y = -86.15649881514048672x -488.5073482818465597024 - 44.75 

y = -86.15649881514048672x - 533.2573482818465597024  .....and rounding, we have

y = -86.156x - 533.257

 

A graph of the solution is found here.........https://www.desmos.com/calculator/zoxdwcc43a

 

Whew!!!   That one was pretty challenging!!!

 

 Aug 22, 2014
 #3
avatar+26396 
+5
Best Answer

 

Find the most left and right tangent

y=ax2a=3.48Point (xp,yp) : (xp=5.67 , yp=44.75)Find the tanget Point (xt,yt)yt=ax2tSlop of y=ax2 is y=2axtSlop of the line through Point p is y=ytypxtxpthe slops must be equal: y=2axt=ytypxtxp2axt(xtxp)=ytyp|yt=ax2t2axt(xtxp)=ax2typ2ax2t2axtxp=ax2typ2ax2tax2t2axtxp+yp=0ax2t2axtxp+yp=0

xt1,2=xp±x2pypayt1,2=ax2t1,2

xt1=5.67+(5.67)2(44.753.48)xt1=5.67+6.70880730103=1.03880730103yt1=3.481.038807301032=3.75533971815right most tangent

xt2=5.67(5.67)2(44.753.48)xt2=5.676.70880730103=12.3788073010yt2=3.48(12.3788073010)2=533.257348282 left most tangent 

heureka Aug 22, 2014

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