13. a) |x - 1| + |y + 3| = 0
x - 1 = 0 /+1
x = 1
y + 3 = 0 /-3
y = -3
b) |2x + 4| + |3y + 9| = 0
2x + 4 = 0 /-4
2x = -4 /:2
x = -2
3y + 9 = 0 /-9
3y = -9 /:3
y = -3
14. a) a + b = -21
a/b = 4/3 ⇔ 3a = 4b ⇒ a = 4b/3
~
a, b = ?
~
a + b = -21
4b/3 + b = -21
(4b + 3b) : 3 = -21
7b/3 = -21 /·3
7b = -63 /:7
b = -9
a = 4b/3 = (-9 · 4) : 3 = -12
b) a · b = 8
a/b = 2 ⇒ a = 2b
~
a, b = ?
~
a · b = 8
2b · b = 8
2b² = 8 /:2
b² = 4
b² = 2²
b = 2
a = 2b = 4
/robertinni