106METHOD I: use cosA = b2 + c2 - a2/2bc
after finding a,b,c using distance formula
METHOD II: cosA = AB.AC/lABl*lACl
Simple find AB vector, AC vector. Take dot product and divide by the product of their magnitudes
calculate the cosine of A in the Δ ABC where A(1,-1,2) B(6,11,2) C(1,2,6)
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3 Answers
106
1CosA=AB.AC/|AB|*|AC|
AB=-5i-12j+ok
AC=0i-3j-4k
AB.AC=0+36+0=36
|AB|*|AC|=√ 25+144+0*√9+16
=13*5=65
CosA= 36/65
