Calculation: 3XTl4U - 1

1

/ d

-

1

/ f

=
-

2

/ R

1

/ d

-

1

/ f

= -

2

/ R

$$\frac{1}{d}-\frac{1}{f}$$ = $$-\frac{2}{R}$$

1

/ d

= -

2

/ R

+

1

/ f

$$\frac{1}{d}$$ = $$-\frac{2}{R}+\frac{1}{f}$$

d =

1

/ (-

2

/ R

+

1

/ f

)

$$d$$ = $$\frac{1}{-\frac{2}{R}+\frac{1}{f}}$$