## Copythat 3 years ago In the figure at right, it is given than BDC is straight, BD = DA, and AB = AC = DC. Find the size of angle C

1. Copythat

|dw:1351641146982:dw|

2. asnaseer

do you know what an isosceles triangle is and what its properties are?

3. Copythat

Yeah. I figured angles B and DAB must be equal, angles CDA and CAD must be equal, and angles B and C must be equal

4. asnaseer

you are almost there - now assign a symbol to angle ABD - lets call it x, and fill-in all the other angles you know using this symbol, e.g. from what you have already said we get: |dw:1351641960334:dw| now find y in terms of x and then use the property of the sum of the angles in a triangle to solve for x.

5. asnaseer

have you understood how to proceed?

6. asnaseer

HINT: Use the angle sum of a triangle in triangle CAD to express y in terms of x.

7. Copythat

Using triangle CAD, y = (180-x)/2?

8. Copythat

I plugged that in for y: 180=3x+[(180-x)/2] And found x=36

9. Copythat

10. asnaseer

yw :)

11. asnaseer

And your answer agrees with the one I got as well :)