You need to use the cosine rule.
a^2=b^2+c^2-2bc(cos A)
2007-01-24 02:18:47 · answer #1 · answered by aepacino 2 · 0⤊ 0⤋
Drop a line from C to c, so that it intersects at a right angle at some point on c. Now, A is stll 68 degrees, b is 7 cm, and your perpendicular line is unknown (call it x). SIN 68=x/7, so 7SIN A = x. The intersection of line x with line c forms two line segments, call them y and z. Line segment y is the one closest to angle A.
Now, once you find x using that method you can say that 7^2-x^2 = y, and determine what y has to be. Subtract y from 15 to get z.
Now you have the lengths of two sides (x and z) of a right triangle with sides a, x, and z, with a the hypoteneuse. So, using Pythagoran's theorem, x^2 + y^2 = z^2, and with only one unknown (a) you can find it. I'll leave the actual math to you.
2007-01-24 10:31:32 · answer #2 · answered by David A 5 · 0⤊ 0⤋