# newbies need sum help..

• Jan 18th 2013, 05:30 AM
jhaycianofficial
newbies need sum help..
hi im engr. Student.. H0pe u help me with this .. Can any0ne s0lve this using law 0f c0sine: (my pr0f. Said that it can be d0ne by the said law)1. If the sl0wer ship in the preseding exercise leaves at noon, and the other at 1p.m., how far apart are they at 2p.m.?2.three circles 0f radii 3,4,and 5 inches respectively are tangent t0 each 0ther externally. Find the angles 0f the triangle f0rmed by j0ining the centers.Can any give the s0luti0n with figure s0 i will understand it .. Tnx in advance :))
• Jan 18th 2013, 09:56 AM
ebaines
Re: newbies need sum help..
For the first problem you've left out some critical data - such as the speed of the two boats - so it's impossible to answer as written.

For the 2nd you know that the 3 sides of the triangle are lengths 7, 8, and 9 - do you see what that is? Now apply the law of cosines:

$C^2 = A^2 + B^2 - 2AB \cos(c)$

You have values for A, B and C, so solve for $\cos(c)$ and hence the angle 'c'. Repeat for angle 'b', and angle 'a' is 180 degrees - c - b.
• Jan 19th 2013, 05:21 PM
jhaycianofficial
Re: newbies need sum help..
For the 2nd you know that the 3 sides of the triangle are lengths 7, 8, and 9 - do you see what that is? Now apply the law of cosines: $C^2 = A^2 + B^2 - 2AB \cos(c)$ You have values for A, B and C, so solve for $\cos(c)$ and hence the angle 'c'. Repeat for angle 'b', and angle 'a' is 180 degrees - c - b.[/QUOTE] CanU please figure it out .. how it the 3 sides became 7,8,9 ?? can u give the figure?
• Jan 19th 2013, 06:30 PM
jhaycianofficial
Re: newbies need sum help..
Quote:

Originally Posted by ebaines
For the first problem you've left out some critical data - such as the speed of the two boats - so it's impossible to answer as written.

For the 2nd you know that the 3 sides of the triangle are lengths 7, 8, and 9 - do you see what that is? Now apply the law of cosines:

$C^2 = A^2 + B^2 - 2AB \cos(c)$

You have values for A, B and C, so solve for $\cos(c)$ and hence the angle 'c'. Repeat for angle 'b', and angle 'a' is 180 degrees - c - b.

Two ships leave a dock at the same time. One sails northeast at the rate 8.5 km/hr. The other sails north at a rate 10 km./hr. how far APART are they at the end of two hours.
• Jan 19th 2013, 06:31 PM
jhaycianofficial
Re: newbies need sum help..
Quote:

Originally Posted by jhaycianofficial
Two ships leave a dock at the same time. One sails northeast at the rate 8.5 km/hr. The other sails north at a rate 10 km./hr. how far APART are they at the end of two hours.

oh im so sorry ..the preceding exercise is THAT !
• Jan 21st 2013, 05:56 AM
ebaines
Re: newbies need sum help..
Quote:

Originally Posted by jhaycianofficial
CanU please figure it out .. how it the 3 sides became 7,8,9 ?? can u give the figure?

If you draw two circles that are tangent to each other (the circles are just touching) you can see that the distance between the centers of the two circles is equal to the sum of their radii.