a. When the denominators are the same, you can just sum the numerators.
Which becomes, 13+2=15--> 15/23
b. Same, when the denominator is the same, you can just minus the numerators. Which becomes, 25-12=13--> 13/27
c. 1kg=1000g. 1000/5=200✖️2=400
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.