Question

$how \: {5}^{k} + 4. {5}^{k} \: change \: into \: {5}^{k \: + \: 1}$
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Answer 1

suppose, 5^k is 'a'

then the equation is a+4a

so a+4a = 5a

now put a= 5^k in the equation

then you'll get

5.5^k

we know,

${x}^{a} \times {x}^{b} = {x}^{a +b }$

${5}^{1} \times {5}^{k} = {5}^{k + 1}$