(18) i did x-3/16 = 2.5/4
40 = 4x - 12
28 = 4x
x = 7

See the attached image to have a look at how the corresponding sides pair up
The red sides pair up to form the ratio (x-3)/2.5
The blue sides pair up to form the ratio 8/2
The similar figures mean that the two ratios are equal

(x-3)/2.5 = 8/2
2(x-3) = 2.5*8
2x-6 = 20
2x = 26
x = 13

Side note: Solving 40 = 4x-12 should lead to 52 = 4x which means x = 13. You subtracted 12 from both sides instead of adding 12 to both sides.

Hello! i hope this
since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.