=> a+b+c+b+c+d+c+d+a+d+a+b=135+173+154+177
=> 3(a+b+c+d)=639
=> a+b+c+d=213
=> d=a+b+c+d-(a+b+c)=78
=> c+a=76
=> b=a+b+c-(c+a)=59
=> a=(d+a+b)-(d+b)=177-(78+59)=40
=> c=135-40-59=36
Vậy a=40; b=59; c=36; d=78
End.
Có:
a+b+c+b+c+d+c+d+a+d+a+b=135+173+154+177
3a+3b+3c+3d=639
3(a+b+c+d)=639
a+b+c+d=213
+)a+b+c+d=135+d=213=>d=78
+)a+b+c+d=a+173=213=>a=40
+)a+b+c+d=154+b=213=>b=59
+)a+b+c+d=177+c=213=>c=36
Ta có: a + b + c = 135
b + c + d = 173
c + d + a = 154
d + a + b = 177
=> a + b + c + b + c + d + c + d + a + d + a + b = 135 + 173 + 154 + 177 = 639
=> 3a + 3b + 3c + 3d = 639
=> 3(a + b + c + d) = 639
=> a + b + c + d = 213
a + b + c = 135 => 135 + d = 213 => d = 78
b + c + d = 173 => a + 173 = 213 => a = 40
c + d + a = 154 => b + 154 = 213 => b = 59
d + a + b = 177 => c + 177 = 213 => c = 36
