suku ke-3 dan suku ke-7 barisa

[tex] u_{3} = a + (3 - 1).b \\ 10 = a + 2b \\ \\ u_{7} = a + (7 - 1).b \\ 22 = a + 6b \\ \\ a + 2b = 10 \\ \frac{a + 6b = 22}{ - 4b = - 12} - \\ b = 3 \\ \\ a + 2b = 10 \\ a + 2(3) = 10 \\ a + 6 = 10 \\ a = 10 - 6 \\ a = 4 \\ \\ s_{n} = \frac{n}{2} (2a + (n - 1) \times b) \\ \\ s_{30} = \frac{30}{2} (2 \times 4 + 29 \times 3) \\ = 15( 8 + 87) \\ = 15 \times 95 \\ = 1.425[/tex]
jawabnnya D
smoga membantuu:D