10: an isosceles base angles are both equal. A triangle has 3 angles. All three angles added equals 180 in every triangle. since one of the base angle is 72 degrees then the other base angle is 72 degrees. ( a triangle has two base angles). so 72+72= 144
180-144= 36 The vertex angle = 36 degrees.
11: angles ratio is 2:4:6. Remember that all angles equal 180. Add the ratio amounts, 2+4+6= 12. Then divide 180 by 12 (180/12 = 15). the smallest angle ratio is 2, so multiply 15 by 2 ( 15 * 2= 30 ) the smallest angle is 30 degrees.
12: all three angles of a triangle adds up to 180. thus, 64 + 74 + x = 180 138 + x = 180 x= 180 - 138 x = 42 x is the third angle. so the third angle is 42 degrees.
