There is an electric lamp with a resistance of 20 ohm. When it works normally, the voltage at both ends is 10 v. but we have 12 V at hand, To connect the lamp to the power supply, how large a resistor needs to be connected in series?

According to series partial pressure:
R / R lamp = (U-U lamp) / u lamp = (12-10) / 10 = 1 / 5
R = R lamp / 5 = 4 Ω
So we need to connect a 4 Ω resistor in series

How to judge the number of zeros in the vertex form of quadratic function
Y = a (X-H) 2 + K. It seems that you can judge several zeros by looking at a and K without Wada's theorem. Great Xia, please tell me how to judge (never tell me about Wada's theorem)

Y = a (X-H) 2 + K. It seems that you can judge several zeros by looking at a and K without Wada's theorem. Great Xia, please tell me how to judge (never tell me about Wada's theorem)
Analysis: when a > 0, k = 0, one; k > 0, none; K

On the distribution of zeros of quadratic function
We know the quadratic equation x ^ 2 + 2mx + 1 = 0 (1) about X. if there are two equations, one of which is in the interval (- 1.0) and the other is in the interval (1.2), find the range of M (2). If both equations are in the interval (0.1), find the range of M. answer (1). F (0) 0 f (1) 0 m = (- 5 / 6, - 1 / 2) (2). If f (1) > 0, f (0) > 0, he > = 0 symmetry axis 0

In the first question, the domain of definition of the solution of the equation is defined in two places, so it can be solved by two inequalities without using the axis of symmetry
In the second question, if there is only one domain of definition where the solution lies, then there may be B ^ 2-4ac > = 0. The first two inequalities are for he > 0. When he = 0, we apply the root formula, x = - B / 2A = m, so we need 0

What's the meaning of zero point of quadratic function

When x is a certain value, the result of the function is y = 0, that is, there is an intersection between the image and the X axis

There is an electric lamp with a resistance of 20 ohm. When it works normally, the voltage at both ends is 10 v. but we have 12 V at hand, To connect the lamp to the power supply, how large a resistor needs to be connected in series?