The combination with repetition equation

In general the formula is: P(n;n1,n2,...,nk) = n! n1! ... Any selection of r objects from A, where each object can be selected more than once, is called a combination of n objects taken r at a time with repetition.

Step-by-step explanation:

< coa = 150 ( given)

as ba and bc are tangents

so oc and oa is perpendicular to cb and ab respectively because in circle normal passes through centre

so in quadrilateral oabc

< coa + < oab + < ocb + < abc = 360

150 +90+90 + < abc = 360

330 + < abc = 360

< abc = 360 -330 = 30

so < abc = 30

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step-by-step explanation: