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@ @XS@ @pý†bɾa@ @

. 36

r +2

24 = 36
r r +2
36r = 24r + 48

12r = 48

r =4 4

.

2x + 7 = 3 [AMC12A 2005]( )

b bx − 10 = −2

2x + 7 = 3 x = −2
2x = 3 − 7 = −4
x = −2
bx − 10 = −2

b(−2) − 10 = −2
−2b = −2 + 10
−2b = 8
. b = −4

3S [AMC10 2001]( )
.S
.

.S = a +b .b a

. 2(a + 3) + 2(b + 3) = 2(a + b) + 12 = 2S + 12