The sum of the first four terms in an arithmetic progression is -18 and the sum of the first six terms is -9. Find the sum of the first ten terms.​

45

Step-by-step explanation:

Let the first term be a and the common difference be d.

So -18=4a+6d and -9=6a+15d. Solving this we get a=-9 and d=3.

So the sum of first 10 terms is 5*(2*(-9)+9*(3))=45

x = 10.1

step-by-step explanation:

all of the angles of a tirangle add up to 180º

180 - 65 = 115 (since we already know the value of one angle)

(2x + 7) + (8x + 7) = 115

(combins like terms) 10x + 14 = 115

(isolate the variable subtract 14 from both sides): 10x = 101

(find the variable divide both sides by 10): x = 101/10

x = 10.1