Q. 1. Suatu barisan aritmatika denganU4+U8+U11+U17=316.Nilai U10 adalah(A) 80(B) 79(C) 78(D) 77(E) 76
Define Terms: Let's denote the first term of the sequence as a and the common difference as d. The nth term of an arithmetic sequence is given by Un=a+(n−1)d.
Write Given Terms: We can write the given terms using the formula for the nth term: U4=a+3dU8=a+7dU11=a+10dU17=a+16d
Add Given Terms: Now, let's add these up as per the given equation:U4+U8+U11+U17=(a+3d)+(a+7d)+(a+10d)+(a+16d)=316
Simplify Equation: Simplify the equation: 4a+36d=316
Introduce Another Equation: We need to find U10, which is a+9d. But we only have one equation and two unknowns. We need another equation to solve for a and d.
Apply Spacing Property: Notice that the terms are evenly spaced, so the sum of pairs equidistant from the ends should be equal. That means U4+U17=U8+U11.
Simplify Equation: Let's write that out:(a+3d)+(a+16d)=(a+7d)+(a+10d)
Subtract Terms: Simplify the equation: 2a+19d=2a+17d
Subtract Terms: Simplify the equation:2a+19d=2a+17d Subtract 2a from both sides:19d=17d