8.6 x10^-9 in standard form

-9 in power means that the value is in fractional and the 10 base is multipied 9 times and put it on denominator.

8.6 = 86 x 10^-1

Let's multiply :

86 x 10^-1 x 10^-9

= 86 x 10^-10

= 86/10000000000

=0,0000000086

Note : if you don't know about how 10^-1 x 10^-9 returns 10^-10, it's because of exponential rules. If the base are same wuth each other, then just do the addition operation in the exponent like this :

10^(-1+(-9))

= 10^(-1-9)

=10^-10

Hope it helps :)

δabc ≅ δdcb by sas because

db ≅ ac . . given (side)

bc ≅ bc . . reflexive property (side)

∠dbc ≅ ∠ acb . . alternate interior angles where transversal bc crosses parallel lines bd and ac (included angle)