# My mind has gone blank!

• Jan 2nd 2008, 06:21 AM
silvermonkey
My mind has gone blank!
"David collected 1p and 2p coins in a jar.
There are 374 coins in the jar.
The coins have a total value of £5.02.
Use algebra to find how many 1p and 2p coins there are in the jar."

"A,B,C and D lie on the circumference of a circle.
AB is parallel to CD.
BC is a diameter.
Prove the the triangles ABC and DCB are congruent."

Help? =)
• Jan 2nd 2008, 06:36 AM
Isomorphism
Quote:

Originally Posted by silvermonkey
"A,B,C and D lie on the circumference of a circle.
AB is parallel to CD.
BC is a diameter.
Prove the the triangles ABC and DCB are congruent."

Help? =)

"My mind has gone blank!" you say?
The problem is a little tricky ;)
Some one might come up with a neater solution.

So I will give you a plan.

1) Draw a diagram!
2) Notice that ABC and BCD are right angled triangles (which are the right angles?)
3) Assuming you know what to do now,are hypotenuses of equal length??
4) Have used the condition that AB || CD ? What can you say about angle CBA and angle BCD? Now what about the remaining angles? Are they equal?
5) We have proved(hopefully you have) some angles equal and some side equal. Which postulate tells you they are congruent?

Answering my questions in the plan,requires little effort.

Hope you get the answer :)