Question

70 баллов дам!!
Помогите решить пожалуйста, кто знает

Answer 1

Ответ:

$1)d = - 8.5 \\ a1 = - 6.8 \\ a5 = a1 + 4d = - 6.8 + 4 \times ( - 8.5) = - 40.8 \\ 2) ....- 6.x. - 2.0...... \\ \\ x = \frac{ - 6 + ( - 2)}{2} = - 4$

$3)a10 = - 10 \: \: \: \: a10 = a1 + 9d\\ a16 = - 19 \: \: \: \: a16 = a1 + 15d\\ \\ a1 + 9d = - 10 \\ a1 + 15d = - 19 \\ a1 + 15d - a1 - 9d = - 19 - ( - 10)\\ 6d = - 9 \\ d = - 1.5$

$4)d = 1.1 \\ a1 = - 7 \\ s8 = \frac{2a1 + 7d}{2} \times 8 = \\ = \frac{2 \times ( - 7) + 7 \times 1.1}{2} \times 8 = \\( - 14 + 7.7) \times 4 = - 6.3 \times 4 = - 25.2$

$5)20.13.6.... \\ a1 = 20 \\ a2 = 13\\ d = 13 - 20 = - 7 \\ a7 = a1 + 6d = \\ = 20 + 6 \times ( - 7) = 20 - 42 = - 22$

$6)100.20.4..... \\ b1 = 100 \\ b2 = 20 \\ q = \frac{b2}{b1} = \frac{20}{100} = \frac{1}{5} \\ b5 = b1 \times {q}^{4} = 100 \times {( \frac{1}{5} )}^{4} = \\ = 100 \times \frac{1}{25 \times 25} = \frac{4}{25} = 0.16$

$7)...3.x.75. - 375.... \\ \\ {x}^{2} = 3 \times 75 \\ x = \sqrt{3 \times 75} = \\ = \sqrt{3 \times 3 \times 5 \times 5} = 3 \times 5 = 15$

$9)b1 = - 3 \\ b(n + 1) = - 4bn \\ b2 = - 4 \times ( - 3) = 12 \\ q = \frac{12}{ - 3} = - 4 \\ s5 = \frac{b1( {q}^{n} - 1)}{ q - 1} = \\ = \frac{ - 3( {( - 4)}^{5} - 1 ) }{ - 4 - 1} = \\ = \frac{3 \times 1024}{5} = 614.4$

$8)b1 = - 6 \\ b(n + 1) = 2bn \\b2 = 2b1 = 2 \times ( - 6 ) = - 12 \\ q = \frac{b2}{b1} = \frac{ - 12}{ - 6} = 2 \\ b6 = b1 \times {q}^{5} = \\ = - 6 \times {2}^{5} = - 6 \times 32 = - 192$

$10) - 1250. - 250. - 50..... \\ q = \frac{ - 250}{ - 1250} = \frac{1}{5} \\ b4 = - 50 \times \frac{1}{5} = - 10 \\ b5 = - 10 = \frac{1}{5} = - 2 \\ s5 = - 1250 - 250 - 50 - 10 - 2 = \\ = 1562$