Which of the following is a true statement a) if ab=cd, then 3cd=3(cd+1). b)if ab=cd, then ab-cd=a-c+b-d. c)if ab=cd, thenab+ef=cd+ef d)if ab=cd, then 2ab=2a+2b

a) if AB = CD, then 3CD = 3(CD + 1) NOT TRUE

example: AB = CD = 1, then 3CD = (3)(1)=3 and 3(CD + 1) = 3(1 + 1) = 3(2) = 6

b) if AB = CD, then AB - CD = A - C + B - D NOT TRUE (it does not make sense because A, B, C and D are points)

c) if AB = CD, then AB + EF = CD + EF TRUE

because

AB = CD    |add EF to both sides

AB + EF = CD + EF

d) if AB = CD, then 2AB = 2A + 2B NOT TRUE (it does not make sense because A and B are points).

= 5

step-by-step explanation:

to find the 15th term substitute n = 15 into the nth term formula

= (- 3 × 15 ) + 50 = - 45 + 50 = 5